Butterflies
Yesterday I visited the American Museum of Natural History in New York
City, for the first time in many years. They have a special exhibit
of butterflies. They get pupae shipped in from farms, and pin the
pupae to wooden racks; when the adults emerge, they get to flutter
around in a heated room that is furnished with plants, ponds of
nectar, and cut fruit.

The really interesting thing I learned was that chrysalises are not
featureless lumps. You can see something of the shape of the animal
in them. (See, for example, this
Wikipedia illustration.) The caterpillar has an exoskeleton,
which it molts several times as it grows. When time comes to pupate,
the chrysalis is in fact the final exoskeleton, part of the animal
itself. This is in contrast to a cocoon, which is different. A
cocoon is a case made of silk or leaves that is not part of the
animal; the animal builds it and lives inside. When you think of a
featureless round lump, you're thinking of a cocoon.

Until recently, I had the idea that the larva's legs get longer, wings
sprout, and so forth, but it's not like that at all. Instead, inside
the chrysalis, almost the entire animal breaks down into a liquid!
The metamorphosis then reorganizes this soup into an adult. I asked
the explainer at the Museum if the individual cells retained their
identities, or if they were broken down into component chemicals. She
didn't know, unfortunately. I hope to find this out in coming weeks.

How does the animal reorganize itself during metamorphosis? How does
its body know what new shape to grow into? It's all a big mystery.
It's nice that we still have big mysteries. Not all mysteries have
survived the scientific revolution. What makes the rain fall and the
lightning strike? Solved problems. What happens to the food we eat,
and why do we breathe? Well-understood. How does the butterfly
reorganize itself from caterpillar soup? It's a big puzzle.

A related puzzle is how a single cell turns into a human baby during
gestation. For a while, the thing doubles, then doubles again, and
again, becoming roughly spherical, as you'd expect. But then stuff
starts to happen: it dimples, and folds over; three layers form, a
miracle occurs, and eventually you get a small but perfectly-formed
human being. How do the cells in the fingers decide to turn into
fingers? How does the cells in the fourth finger know they're one
finger from one side of the hand and three fingers from the other
side? Maybe the formation of the adult insect inside the chrysalis
uses a similar mechanism. Or maybe it's completely different. Both
possibilities are mind-boggling.

This is nowhere near being the biggest pending mystery; I think we at
least have some idea of where to start looking for the answer.
Contrast this with the question of how it is we are conscious, where
nobody even has a good idea of what the question is.

Other caterpillar news: chrysalides are so named because they often
have a bright golden sheen, or golden features. (Greek "khrusos" is
"gold".) The
Wikipedia picture of this is excellent too. The "gold" is a
yellow pigmented area covered with a shiny coating. The explainer
said that some people speculate that it helps break up the outlines of
the pupa and camouflage it.

I asked if the chrysalis of the viceroy butterfly, which, as an adult,
resembles the poisonous monarch butterfly, also resembled the
monarch's chrysalis. The answer: no, they look completely different.
Isn't that interesting? You'd think that the pupa would get at least
as much benefit from mimicry as the adult. One possible explanation
why not: most pupae don't make it to adulthood anyway, so the marginal
benefit to the species from mimicry in the pupal stage is small
compared with the benefit in the adult stage. Another: the pupa's
main defense, which is not available to the adult, is to be difficult
to see; beyond that it doesn't matter much what happens if it
is seen. Which is correct? I don't know.

For a long time folks thought that the monarch was poisonous and the
viceroy was not, and that the viceroy's monarch-like coloring tricked
predators into avoiding it unnecessarily. It's now believed that
both speciies are poisonous and bad-tasting, and that their
similar coloring therefore protects both species. A predator who eats
one will avoid both in the future. The former kind of mimicry is
called Batesian; the latter, Müllerian.

The monarch butterfly does not manufacture its toxic and bad-tasting
chemicals itself. It is poisonous because it ingests poisonous
chemicals in its food, which I think is milkweed plants. Plant
chemistry is very weird. Think of all the poisonous foods you've ever
heard of. Very few of them are animals. (The only poisonous meat I
can think of offhand is the liver of arctic animals, which has a
toxically high concentration of vitamin D.) If you're stuck on a
desert island, you're a lot safer eating strange animals than you are
eating strange berries.